Bacteria

Staphylococcal Infections

Skin

Organism: Staphylococcus aureus

• Invasion through hair follicle (foliculitis) or pimples

  • Sty: infected follicle of eyelash

  • Boil: (furuncle) deeper pus-filled infection 

  • Carbuncle: further spread of infection 

• Pathogenicities: 

  • prevent movement of phagocytic cells to site of infection 

  • Leukostatin: kills macrophages with leukocidin 

  • Coagulase + 

  • Peptidoglycan Layer - resists digestion by lysosome

  • May act as super antigen 

• Can get repeat infections with organism even though antibodies are present

• Hospital personnel can often spread infections - asymptomatic carriers (50% of adult are nasal carriers) 

  • Methicillin resistant staph aureus 

Impetigo

• Skin

• Organism: Staphylococci or Streptococcus pyogenes (can cause strept throat) (sometime mixed infections)

• very common in children

• pyoderma lesions - skin sores

Scalded Skin Syndrome

• Skin

• Organism: S. aureus

• Exotoxins:

  • Exfoliative toxin A and B

    • one is produced from plasmid other is carried on chromosome

    • Toxin B - carried in circulation to all areas of skin can be damaged from exfoliatin

  • Cause of impetigo in newborn (pemphigus neonatorum)

Toxic Shock Syndrome 

• Skin

• Organism: Staph Aureus 

• Can be life threatening since it can lead to sock and organ failure

• Exotoxin: 

  • Toxin (TSST-1) - gets released into circulation and acts as superantigen

Streptococcal Infections

• Skin

• Organism: Streptococcus pyogenes - reffered to as group A streptococci (GAS)

• Virulence Factors

  • hemolysins

  • Streptolysins

  • M protiens

  • Capsules

  • streptokinases

  • hyaluronidase

  • deoxyribonucleases

Streptococcal Infections Diseases

• Skin

• causes strep throat + scarlet fever rash (caused by Erythrogenic toxin -carried on prophage)

• Complication - Rheumatic Fever

• Other diseases:

  • Erysipelas

  • Necrotizing Fasciitis -flash eating bacteria

  • Streptococcal Toxic Shock Syndrome

Acne

• Skin

• Organism: Propionbacterium acnes (anaerobic)

• Sebaceous glands secrete more oil onto skin, organisms can multiply to greater degree since they have more nutrients oil for growth 

• Overgrowth can lead to skin pores being clogged and inflamed - tissue destruction

Pseudomonas Dermatitis 

• Skin

• Organism: Pseudomonads (often Pseudomonas aeruginosa) (gram neg) 

• highly resistant to antibiotics and disinfectants

• Makes several Exotoxins

• Grows in biofilm

• Makes Endotoxins

• causes infections in burn patients